1. Field of the Invention
The present invention generally relates an androgynous, reconfigurable closed loop feedback controlled low impact docking system and assembly with load sensing electromagnetic capture ring. More particularly, the invention relates to a load sensing, electromagnetic docking system. Still more particularly, the invention relates to a docking assembly and system having a reconfigurable control system that permits a load sensing ring with an electromagnetic capture mechanism to xe2x80x9csoftlyxe2x80x9d capture and dock two structures or vehicles together.
2. Background of the Invention
Docking systems permit two structures or vehicles to be coupled together. For instance, the assignee of the present invention uses docking systems to dock one spacecraft to another in orbit around the Earth. The International Space Station (ISS) currently under construction in space has a docking system to permit the Space Transport System (STS), also referred to as the xe2x80x9cShuttlexe2x80x9d, to dock to the ISS. Crew, equipment, supplies, and other types of cargo then can be transferred from one vehicle to the other through the docking system tunnel.
Most docking systems use a mechanical structure comprising latches, hooks and other mechanisms. Generally, there are two different ways of coupling vehicles together, either docking or berthing. xe2x80x9cDockingxe2x80x9d occurs when a free-flying vehicle, such as the Space Shuttle, under its own control maneuvers into the capture envelope and then into contact with the docking assembly of another vehicle, such as the Space Station. xe2x80x9cBerthingxe2x80x9d occurs when an externally attached device such as a Remote Manipulator System (RMS), that is structurally grounded to one vehicle such as the Space Station, attaches to the other vehicle and maneuvers into the capture envelope and then into contact with the Space Station docking assembly. Docking or berthing two vehicles requires that each vehicle have a docking assembly. To dock two vehicles using a conventional mechanical docking assembly, the vehicles must be pressed together with sufficient force to re-align the soft capture ring and to trip the mechanical soft capture latches, hooks, or etc. on the respective docking assemblies, thereby coupling the two docking assemblies. In a terrestrial application, this action is analogous to two train cars coupling. Train cars can be coupled only if one car is pushed against the other car with enough force to open and then close the mechanical coupling assembly.
The following discussion details the primary phases in any docking scenario. First is the xe2x80x9capproachxe2x80x9d phase wherein a vehicle moves into a capture envelope. A capture envelope is a predetermined area surrounding a docking assembly into which a pilot or remote control must guide a vehicle before docking/berthing can be effected. Second is the xe2x80x9calignmentxe2x80x9d phase wherein the two vehicles to be docked establish a soft capture ring alignment with one another. This phase has traditionally been accomplished by driving vehicles together to force capture ring alignment using passive guides during docking or by realigning using RMS visual cues to correct for misalignments. Third is the xe2x80x9ccapturexe2x80x9d phase which is accomplished by forcing capture latches to hold the vehicles together or by xe2x80x9creach around and grab armsxe2x80x9d to capture the mating interface during berthing. Fourth is the xe2x80x9cattenuationxe2x80x9d phase, wherein the dynamic energy and residual motion of the separate vehicles is absorbed by the combined assembly. Fifth is the xe2x80x9cretractionxe2x80x9d phase where residual misalignments are nullified and the docking mechanism is retracted to bring the mating sealing interfaces in contact. The final phase is the xe2x80x9cstructural matingxe2x80x9d phase. There, structural latches are engaged to provide a rigid structural interface and to compress and pre-load the seals to facilitate the maintenance of a pressurized volume.
With prior mechanical docking assemblies, the action of forcing two vehicles together, particularly in space, can result in damage to one or both of the vehicles or sensitive systems and components due to the high forces required to actuate capture mechanisms when docking. Further, forcing the vehicles together can ruin vibration sensitive experiments, such as crystal growth experiments, that may be performed on one or both of the vehicles. Thus, there is a need for a docking system that can minimize or eliminate the potential for structural damage and vibration caused by conventional docking systems.
Despite the advantages a docking system would provide, to date no such docking system is known to exist that provides low force mating or that can accomplish both docking and berthing operations.
The problems noted above are solved in large part by the androgynous, reconfigurable closed loop feedback controlled low impact docking system with load sensing electromagnetic capture ring of the present invention. In one embodiment, the docking system comprises two fully androgynous docking assemblies. This allows two identical docking assemblies to dock or berth with one another in contrast to docking systems that use different (male and female) assemblies. Each docking assembly comprises a load sensing ring having an outer face, one or more electromagnets positioned on the outer face of the load sensing ring, and striker plates positioned on the outer face of the load sensing ring. Each docking assembly further comprises a plurality of load cells coupled to the load sensing ring, a plurality of actuator arms coupled to the load sensing ring capable of dynamically adjusting the position and orientation of the load sensing ring, and a reconfigurable closed loop control system capable of analyzing signals originating from the load cells and of outputting real time control for the actuator arms.
To a certain extent, the docking system of the present invention is somewhat analogous to the Russian built Androgynous Peripheral Assembly System (APAS). The docking system disclosed herein differs, however, from the APAS in that the present invention is a xe2x80x9csmartxe2x80x9d electromechanical system comprised of a blend of structural/mechanical, electrical, computer controlled, and software elements. Further, xe2x80x9candrogynousxe2x80x9d as that term is used in the Russian APAS system means that only parts of the assembly interfaces are androgynous, whereas the present invention is fully androgynous. Being fully androgynous allows an active docking assembly to mate with another active docking assembly; two active APAS systems cannot mate.
In addition, the design of the present invention varies from the traditional docking mechanism of a highly mechanically interconnected system of gears, clutches, and linkages. The present invention comprises a reconfigurable computer controlled mechanism and uses a smart electromechanical, six (6) degrees of freedom platform that incorporates an active load sensing system to automatically and dynamically adjust the soft capture ring during capture, instead of requiring significant force to push and realign the ring. Instead of mechanical trip latches that require a tripping force for capture, the present invention uses electromagnets to achieve xe2x80x9csoftxe2x80x9d capture, but not limited to. Further, the present invention also can be controlled as a damper in lieu of the interconnected linear actuators and the separate load attenuation system associated with conventional docking systems, which are used to attenuate the residual motion and dissipate the forces resulting from ramming two vehicles together.
Moreover, the docking assembly of the present invention does not require minimum or maximum closing velocities or dynamic forces for correcting misalignments and effective capture. In fact, the docking system of the present invention can handle large positive closing velocities and forces, as well as negative and zero closing velocities. Further, the reconfigurable closed loop control system is adjustable to match a specific vehicle""s properties i.e. mass and center of mass or gravity offset and operational mating characteristics, i.e., approach velocities and angular rates. The control system parameters are tunable in each axis to various stiffness and damping constants depending upon stiffness, capture, and mass handling response requirements. This results in a large range of vehicle applicability and mating capabilities.